Encoderless motor with improved granularity and methods of use

Abstract

A DC electric motor having a stator mounted to a substrate, the stator having a coil assembly having a magnetic core, a rotor mounted to the stator with permanent magnets distributed radially about the rotor, the permanent magnets extending beyond the magnetic core, and sensors mounted to the substrate adjacent the permanent magnets. During operation of the motor passage of the permanent magnets over the sensors produces a substantially sinusoidal signal of varying voltage substantially without noise and/or saturation, allowing an angular position of the rotor relative the substrate to be determined from linear portions of the sinusoidal signal without requiring use of an encoder or position sensors and without requiring noise-reduction or filtering of the signal.

What is claimed: 
     
       1. A DC electric motor comprising:
 a stator mounted to a substrate, the stator comprising a coil assembly having a core of magnetic material and electrical windings; 
 a rotor mounted to the stator, the rotor comprising permanent magnets mounted to a cylindrical skirt and each extending to a distal edge; and 
 a plurality of sensors mounted to the substrate adjacent the permanent magnets, wherein a displacement of the motor is determinable from signals from the plurality of sensors; 
 wherein a clearance between the extended distal edge of each of the permanent magnets and the plurality of sensors is defined such that during operation of the motor, passage of the permanent magnets over the plurality of sensors produces a plurality of sinusoidal signals of varying voltages; 
 a processor module communicatively coupled with the plurality of sensors and configured to:
 receive the plurality of sinusoidal signals from the plurality of sensors, during rotation of the rotor, to produce a signal pattern comprising an intersecting superimposition of the plurality of sinusoidal signals, each sinusoidal signal including one or more portions between crossing points of the signal pattern that are substantially straight line segments; and 
 determine a displacement of the motor based on at least one of the one or more portions between the crossing points of the signal pattern that are substantially straight line segments. 
 
 
     
     
       2. The system of  claim 1 , wherein the plurality of sensors mounted to the substrate are positioned relative the extended edge of the permanent magnets, with the clearance from the extended edge of the permanent magnets to the plurality of sensors sufficient to provide a voltage of from about 2 to about 5 volts DC. 
     
     
       3. The system of  claim 2 , wherein the extended edge of the permanent magnets extend beyond a distal extremity of the coil assembly by about 1 mm or more. 
     
     
       4. The system of  claim 1 , wherein the plurality of sensors are linear Hall-effect sensors, spaced apart by a common arc length along an arcuate path of the rotor. 
     
     
       5. The system of  claim 4 , comprising an even number of permanent magnets evenly spaced around the cylindrical skirt with adjacent magnets exhibiting opposite polarity at the distal edge of the skirt, and three Hall-effect sensors, each Hall-effect sensor producing a voltage varying in a substantially sinusoidal pattern, the three patterns phase-shifted by about degrees when the motor is in operation. 
     
     
       6. The system of  claim 5 , comprising twelve magnets and three linear Hall-effect sensors spaced at increments of forty degrees of mechanical rotation. 
     
     
       7. The system of  claim 5 , wherein intersections of adjacent sinusoidal patterns define the substantially straight line segments. 
     
     
       8. The system of  claim 6 , wherein the substrate is a printed circuit board (PCB) comprising circuitry enabling analog-to-digital conversion (ADC) of voltage values in the defined linear portions of the patterns, and zero-crossing detection of the analog voltage patterns. 
     
     
       9. The system of  claim 8 , wherein the circuitry employs an 11-bit analog to digital converter (ADC), producing 2048 equally-spaced digital values for each linear portion of the patterns. 
     
     
       10. The system of  claim 8 , wherein the circuitry is implemented in a programmable system on a chip (PSOC). 
     
     
       11. A method for encoding a DC electric motor, comprising:
 mounting a stator to a substrate, the stator comprising a coil assembly having a core of magnetic material and electrical windings; 
 mounting a rotor to the stator, the rotor comprising permanent magnets mounted to a cylindrical skirt with each of the permanent magnets extending to a distal edge; 
 positioning a plurality of sensors on the substrate adjacent the permanent magnets, wherein a displacement of the motor is determinable from signals from the plurality of sensors; 
 operating the DC electric motor by commutation, causing the permanent magnets to pass over the plurality of sensors, producing a plurality of sinusoidal signals of varying voltages from which a signal pattern comprising an intersecting superimposition of the plurality of sinusoidal signals is formed, each sinusoidal signal including one or more portions between crossing points of the signal pattern that are substantially straight line segments; and 
 determining positions of the rotor based on at least one of the one or more portions between crossing points of the signal pattern that are substantially straight line segments. 
 
     
     
       12. The method of  claim 11 , wherein the plurality of sensors mounted to the substrate are positioned relative to the extended edge of the permanent magnets of the rotor, with the clearance from the extended edge to the plurality of sensors sufficient to provide a voltage of from about 2 to about 5 volts DC. 
     
     
       13. The method of  claim 12 , wherein the extended edge of the permanent magnets extend beyond the distal extremity of the coil assembly by about 1 mm or more. 
     
     
       14. The method of  claim 11 , wherein the plurality of sensors are linear Hall-effect sensors, spaced apart by a common arc length along an arcuate path of the rotor. 
     
     
       15. The method of  claim 14 , comprising an even number of permanent magnets evenly spaced around the cylindrical skirt with adjacent magnets exhibiting opposite polarity at the distal edge of the skirt, and three Hall-effect sensors, each Hall-effect sensor producing a voltage varying in a substantially sinusoidal pattern, the three patterns phase-shifted by about 120 degrees. 
     
     
       16. The method of  claim 15 , comprising twelve magnets and three linear Hall-effect sensors spaced at increments of about twenty degrees of mechanical rotation. 
     
     
       17. The method of  claim 15 , wherein intersections of adjacent sinusoidal patterns define the substantially straight line segments. 
     
     
       18. The method of  claim 16 , wherein the substrate is a printed circuit board (PCB) comprising circuitry enabling analog-to-digital conversion (ADC) of voltage values in the defined linear portions of the patterns, and zero-crossing detection of the analog voltage patterns, wherein the circuitry is implemented in a programmable system on a chip (PSOC). 
     
     
       19. The method of  claim 18 , wherein the circuitry employs an 11-bit analog to digital converter, producing 2048 equally-spaced digital values for each linear portion of the patterns. 
     
     
       20. A motor system comprising:
 a stator comprising a magnetic core; 
 a rotor that is rotatably mounted relative to the stator, the rotor having a plurality of permanent magnets distributed radially about the rotor with each magnet extending to a distal edge that extends beyond the magnetic core; 
 a plurality of sensors at fixed positions relative the stator and disposed adjacent a path of the plurality of magnets during rotation of the rotor, wherein a clearance is defined between the distal edges of the plurality of permanent magnets and each of the plurality of sensors such that during operation of the motor, passage of the permanent magnets over the plurality of sensors produces a plurality of intersecting substantially sinusoidal signals of varying voltage such that a displacement of the motor is determinable based, at least in part, on signal from a sensor of the plurality of sensors; and 
 a processor module communicatively coupled with the plurality of sensors and configured to: 
 receive the plurality of sinusoidal signals from the plurality of sensors during rotation of the rotor to produce a signal pattern comprising an intersecting superimposition of the plurality of sinusoidal signals, each sinusoidal signal including one or more portions between crossing points of the signal pattern that are substantially straight line segments; and 
 determine a displacement of the motor based on at least one of the one or more portions between the crossing points of the signal pattern that are substantially straight line segments.